JP2002025580A - Proton conductive film for fuel cell and fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a proton conductive film for fuel cells, having hydrophilic nature and easy to contact the electrode interface. SOLUTION: The proton conductive film for fuel cells consists of a film sulfonated by normal pressure discharging plasma processing. In a sulfonating processing method, counter electrodes, constructed with a pair of electrodes countered each other, and formed by covering one or both opposite faces of the electrodes with a solid dielectrics and arranged under the vicinity of the atmospheric pressure of a mixed gas atmosphere which consists of sulfur oxide gas and oxygen and/or rare gas, are applied with a specific pulse voltage in a state that the proton conductive film for fuel cells is arranged between the counter electrodes, to put the proton conductive film for fuel cells under an atmospheric pressure discharging plasma processing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a sulfonated proton conductive membrane for a fuel cell, a method for sulfonating a proton conductive membrane for a fuel cell, and a sulfonated proton conductive membrane for a fuel cell. And a fuel cell using the same.

[0002]

2. Description of the Related Art Fuel cells are different from conventional internal combustion engines.
Because of its low load, high power generation efficiency and low pollution, it has excellent environmental properties and is expected to be a next-generation power generation device that can contribute to solving environmental and energy problems that are currently major issues. I have. Fuel cells are classified into several types depending on the type of electrolyte and fuel, such as an alkaline aqueous solution type, a phosphoric acid electrolyte type, a molten carbonate type, a solid oxide type,
Solid polymer fuel cells, direct methanol fuel cells, and the like can be mentioned. Among them, solid polymer fuel cells are smaller and have higher output than any other method, and are small-scale on-site fuel cells and mobile bodies ( It is considered to be the mainstay of the next generation as a fuel cell for (in-vehicle) and portable use.

The structure of a polymer electrolyte fuel cell is basically a sandwich structure composed of a separator to which hydrogen is supplied, a fuel electrode, an ion exchange membrane, an air electrode, and a separator to which air is supplied. Consists of stacked stacks.

At present, the polymer electrolyte fuel cell has not yet reached the practical stage. However, as a fuel cell used in the trial production or the test stage, a perfluoroalkylene has a main skeleton and a part of the electrolyte membrane has a main skeleton. A fluorine-based membrane having an ion exchange group such as a sulfonic acid group or a carboxylic acid group at the terminal of a side chain of perfluorovinyl ether is mainly used as a proton conductive membrane. Examples of such a fluorine-based film include a Nafion film of Du Pont described in US Pat. No. 4,330,654 and the like;
Dow Che described in 366137
Dow film manufactured by Asahi Chemical Co., Ltd., and Acipl manufactured by Asahi Kasei Kogyo Co., Ltd.
An ex film, a Flemion film manufactured by Asahi Glass Co., Ltd., and the like are known.

It is desired that these fluorine-based films have high contact with the electrode interface. Also, because the water generated by the reaction inhibits the ion exchange membrane, the membrane itself retains water,
If hydrophilicity can be imparted, the performance of the fuel cell will be improved. Therefore, development of a technology for imparting such functions is desired.

[0006]

SUMMARY OF THE INVENTION In view of the above, the present invention provides a proton conductive membrane for a fuel cell which has hydrophilicity and good compatibility with an electrode interface, and provides a fuel cell with high power generation efficiency and long life. It is intended to be realized.

[0007]

Means for Solving the Problems As a result of intensive studies in view of the above problems, the present inventor has found that by performing sulfonation by a discharge plasma treatment method capable of realizing a stable discharge state under atmospheric pressure conditions, The present inventors have found that the proton conductive membrane for a fuel cell can be easily made hydrophilic, and have completed the present invention.

[0008] That is, a first aspect of the present invention (the invention of claim 1) is that the proton conductive membrane for a fuel cell is characterized by comprising a proton conductive membrane for a fuel cell which has been sulfonated by normal pressure discharge plasma treatment. It is.

The second aspect of the present invention (the invention of claim 2)
The normal-pressure discharge plasma treatment comprises a pair of electrodes facing each other, and a counter electrode having one or both of the electrodes facing each other coated with a solid dielectric is provided with a sulfur oxide gas and oxygen and / or In a state where the mixed gas atmosphere composed of a rare gas is arranged near the atmospheric pressure and the proton conductive membrane for a fuel cell is arranged between the opposed electrodes, a pulse rise time of 20 μs or less and a pulse duration time between the opposed electrodes are set. 1 to
50 μs, frequency 1-20 kHz, electric field strength 50-
By applying a pulse voltage of 100 kV / cm,
The method according to claim 1, wherein atmospheric pressure discharge plasma treatment is performed on the proton conductive membrane for a fuel cell.

The third aspect of the present invention (the invention of claim 3)
Is a fuel cell characterized by using the proton conductive membrane for a fuel cell obtained by the sulfonation treatment method according to the first or second invention.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for sulfonating a proton conductive membrane for a fuel cell to impart hydrophilicity or the like by a normal pressure discharge plasma treatment. More specifically, the present invention relates to a method under a pressure near atmospheric pressure. A solid dielectric is provided on at least one surface facing the counter electrode, and a proton conductive membrane for a fuel cell is disposed between the counter electrode and the solid dielectric or between the solid dielectrics. The method is characterized in that a pulse electric field is applied between the opposed electrodes below.

Even if the proton conductive membrane for a fuel cell used in the present invention has irregularities on the surface due to its structure, the surface treatment method of the present invention can be applied to any object having irregularities. This method can be applied stably without giving any damage, and is a simpler method than the conventional method of dipping in a solution because the treatment is performed by gas.

The above-mentioned pressure near the atmospheric pressure is defined as 1.333.
× 10 ^{4 to} 10.664 × 10 ⁴ Pa. 9.331 × 10 ^{4 for} easy pressure adjustment and simple equipment
It is preferably in the range of 10.397 × 10 ⁴ Pa.

[0014] The surface treatment method of the present invention is performed in an apparatus having a pair of opposed electrodes and a solid dielectric placed on at least one of the opposed surfaces of the electrodes. The portion where plasma is generated is between the solid dielectric and the electrode when a solid dielectric is installed on one of the electrodes, and between the solid dielectrics when the solid dielectric is installed on both of the electrodes. Space. The treatment is performed by disposing a proton conductive membrane for a fuel cell, which is an object to be processed, between the solid dielectric and the electrode or between the solid dielectrics.

Examples of the electrodes include those made of a simple metal such as copper and aluminum, alloys such as stainless steel and brass, and intermetallic compounds. It is preferable that the counter electrode has a structure in which the distance between the counter electrodes is substantially constant in order to avoid occurrence of arc discharge due to electric field concentration. Examples of an electrode structure that satisfies this condition include a parallel plate type, a cylindrical opposed plate type, a spherical opposed plate type, a hyperboloid opposed plate type, and a coaxial cylindrical structure.

The solid dielectric is provided on one or both of the opposing surfaces of the electrode. At this time, the electrode on the side on which the solid dielectric is placed is in close contact with the electrode, and the opposing surface of the contacting electrode is completely covered. This is because if there is a portion where the electrodes directly face each other without being covered by the solid dielectric, an arc discharge occurs therefrom.

The shape of the solid dielectric may be a sheet or a film, but preferably has a thickness of 0.01 to 4 mm. If the thickness is too large, a high voltage is required to generate discharge plasma. If the thickness is too small, dielectric breakdown occurs when a voltage is applied, and arc discharge occurs.

As the material of the solid dielectric, for example,
Plastics such as polytetrafluoroethylene and polyethylene terephthalate; glass; silicon dioxide; aluminum oxide; zirconium dioxide; metal oxides such as titanium dioxide; and double oxides such as barium titanate.

It is preferable that the solid dielectric has a relative dielectric constant of 2 or more (the same applies in an environment of 25 ° C.).
Specific examples of the dielectric having a relative dielectric constant of 2 or more include polytetrafluoroethylene, glass, and a metal oxide film. In order to stably generate a high-density discharge plasma, it is preferable to use a fixed dielectric having a relative dielectric constant of 10 or more. Although the upper limit of the relative permittivity is not particularly limited, it is known that the actual material is about 18,500. As a solid dielectric having a relative dielectric constant of 10 or more, a metal oxide film mixed with 5 to 50% by weight of titanium oxide and 50 to 95% by weight of aluminum oxide;
Alternatively, it is preferable to use a metal oxide film containing zirconium oxide and having a thickness of 10 to 1000 μm.

The distance between the electrodes is determined by the thickness of the solid dielectric,
It is appropriately determined in consideration of the magnitude of the applied voltage, the purpose of utilizing the plasma, and the like, and is preferably 1 to 50 mm. If it is less than 1 mm, it may not be sufficient to place the electrodes at intervals, and if it is more than 50 mm, it is difficult to generate uniform discharge plasma.

A discharge plasma is generated by applying a pulse electric field between the electrodes. FIG. 1 shows an example of a pulse waveform. (A) and (B) are impulse waveforms, (C) is a square wave waveform, and (D) is a modulation waveform. Further, FIG. 1 shows only a waveform in which voltage application is a repetition of positive and negative, but a waveform having a single wave in which a voltage is applied to either the positive or negative polarity side may be used.

The pulse electric field applied between the electrodes has a voltage rise time of 20 μs or less and an electric field strength of 50 to 1
It is preferably set to 00 kV / cm. Applying such a high-speed pulse leads to the generation of high-density plasma, and is important for achieving high-speed continuous processing. Here, the rise time refers to a time during which the voltage change is continuously positive.

The shorter the rise time of the pulse electric field is, the more efficiently the gas is ionized during the generation of the plasma. If the rise time of the pulse exceeds 20 μs, the discharge state easily shifts to an arc and becomes unstable. And a high-density plasma state cannot be expected. Further, it is better that the rise time is short. However, there is a limit to a device that has an electric field intensity large enough to generate plasma at normal pressure and generates a short rise time electric field. It is difficult to achieve a pulsed electric field with a rise time of less than. More preferably, the rise time is 50 ns to 5 μs.

It is preferable that the fall time of the pulse electric field is also steep.
The time scale is preferably equal to or less than s. For example, in the power supply device used in the embodiment of the present invention, the rise time and the fall time can be set to the same time, although it differs depending on the pulse electric field generation technique.

The frequency of the pulse electric field is preferably 1 to 20 kHz. When the frequency is less than 1 kHz, the processing takes too much time due to the low plasma density, and when the frequency exceeds 20 kHz, arc discharge tends to occur. By applying such a high-frequency pulsed electric field, the processing speed can be greatly improved.

It is preferable that the pulse duration in the pulse electric field is 1 to 50 μs. If it is less than 1 μs, the discharge becomes unstable, and if it exceeds 50 μs, it becomes easy to shift to arc discharge. More preferably,
3 μs to 20 μs. Here, the pulse duration, which is shown in FIG. 2 as an example, refers to a time during which a pulse is continuous in a pulse electric field composed of repetition of ON and OFF. In the case of the intermittent pulse as shown in FIG. 2A, the pulse duration is equal to the pulse width time, but in the case of the pulse having the waveform as shown in FIG. Say time including.

Further, in order to stabilize the discharge, it is preferable to have an OFF time lasting at least 1 μs within a discharge time of 1 ms.

The above discharge is performed by applying a voltage.
Although the magnitude of the voltage is appropriately determined, in the present invention,
It is preferable that the electric field strength between the electrodes is in a range of 50 to 100 kV / cm. If it is less than 5 kV / cm, it takes too much time for the treatment, and if it exceeds 100 kV / cm, arc discharge is likely to occur. In applying the pulse voltage, a direct current may be superimposed.

In the sulfonation of the present invention, a mixed gas composed of a sulfur oxide gas and oxygen and / or a rare gas is present as a gas (hereinafter referred to as a processing gas) existing in the discharge plasma generation space.

Examples of the sulfur oxide gas as the processing gas include sulfur dioxide, sulfur trioxide gas, and vaporized gas of sulfuric acid. The sulfur oxide gas is used not as a single atmosphere but as a mixed gas with oxygen and / or a rare gas from the viewpoint of safety and economy.

As the rare gas, neon, argon,
A rare gas such as xenon is used. These alone are 2
Mixtures of more than one species may be used. When a rare gas and / or oxygen is used, it is preferable that the ratio of the processing gas be 1 to 10% by volume. Alternatively, plasma discharge may be performed in an atmosphere composed of the rare gas to generate radicals on the surface, and then the radical may be brought into contact with the processing gas.

As an atmosphere gas, a compound having more electrons is more advantageous in increasing the plasma density and performing high-speed processing. Therefore, the most desirable choice in consideration of availability, economy and processing speed is argon.

Conventionally, at a pressure close to the atmospheric pressure, the treatment has been performed in an atmosphere in which helium is present in a large excess. However, according to the method using argon of the present invention, the treatment is more stable than helium. Processing is possible, and furthermore, by performing the processing in the presence of these gases having a large molecular weight and more electrons, a high-density plasma state can be realized and the processing speed can be increased. Has superiority.

The surface treatment of the present invention may be carried out by heating or cooling the object to be treated, but is sufficiently possible at room temperature.
The time required for the above-described processing is appropriately determined in consideration of the applied voltage, the type of the processing gas, the ratio in the mixed gas, and the like.

In the present invention, a stable discharge plasma can be continuously generated irrespective of the gas atmosphere by arranging a solid dielectric between the opposing electrodes and applying a pulsed electric field. . Therefore, the reactive gas and the shape of the electrode can be freely designed. Further, by using a high-speed pulse electric field, a high-density plasma state is realized, and high-speed and high-level processing can be performed.

It is considered that by applying the pulse electric field, a cycle in which the discharge is stopped before the discharge state shifts to the arc and the discharge is started again is realized, and a stable discharge state is maintained as a whole. Furthermore, by applying a pulse electric field having a steep rising, gas molecules existing in the space can be efficiently excited,
It is considered that a state is realized in which the absolute number of molecules in the ionized state in the space is large, that is, the plasma density is high.

[0037]

EXAMPLES The present invention will be described in more detail based on examples, but the present invention is not limited to these examples. The processing apparatus used in the examples is as follows.

As shown in FIG. 3, the processing vessel 1, counter electrodes (upper electrode 2 and lower electrode 3), pulse power supply 4, gas supply device 5, oil rotary pump 6, unwinder 7, and winder 8 Was used.

The processing container 1 has an inlet 11 for a substrate to be processed.
And a base material outlet 12. Further, the processing container 1 is provided with a gas inlet 13 and a gas outlet 14, the gas inlet 13 is connected to the gas supply device 5, and the gas outlet 14 is provided with an oil rotary pump 6 for reducing pressure. It is connected.

In the processing vessel 1, an upper electrode 2 and a lower electrode 3 are provided at a predetermined interval. The upper electrode 2 is electrically connected to a pulse power source 4 and the lower electrode 3 is grounded, and applies a pulse voltage between the upper electrode 2 and the lower electrode 3.

The unwinding machine 7 is wound with a proton conductive membrane P for processing. The proton conductive membrane P travels between the upper electrode 2 and the lower electrode 3 by a transport system including the feed rolls 9 and 10 and the winder 8.

By operating the gas supply device 5 and the oil rotary pump 6, the gas in the processing container 1 is discharged from the discharge port 14, and the processing gas whose flow rate has been adjusted is introduced into the processing container 1 from the gas inlet 13. Then, the inside of the processing vessel 1 is set to a processing gas atmosphere under a pressure close to the atmospheric pressure, and in this state, the upper electrode 2
A glow discharge plasma is generated by applying a pulse voltage from a pulse power source 4 between the upper electrode 2 and the lower electrode 3, and the proton conductive film P is caused to run between the upper electrode 2 and the lower electrode 3. The sulfonation of the proton conductive membrane P can be performed continuously.

Here, in FIG. 3, the counter electrode (upper electrode 2
And only one set of the lower electrode 3) is shown, but if necessary, a large number of sets of counter electrodes are grounded to increase the contact distance of the proton conductive film P with the atmospheric pressure discharge plasma. P may be run at high speed. In addition, the material of the processing container 1 is not particularly limited, and examples thereof include resin, glass, and metal.

Example 1 In the processing apparatus shown in FIG. 3, an upper electrode 2 (SU) coated with a sprayed film of Al ₂ O ₃ (solid dielectric) by 1.5 mm was used.
S304, size 120 mm x 50 mm) and lower electrode 3 (SUS304, size 120 mm x 50 mm)
The distance between the electrodes is 2 mm, and the proton conductive membrane Nafion 117 for the fuel cell is provided in the space between the upper and lower electrodes.
(Manufactured by Du Pont) was placed.

Next, after the internal pressure of the processing chamber 1 by an oil rotary pump 6 was evacuated to a 1.333 × 10 ² Pa, from 2 vol% SO _2/30 vol% O _2/68 volume% Ar In the state where the mixed gas is introduced from the gas inlet 13 until the inside of the container reaches atmospheric pressure, a pulse wave type is applied between the upper electrode 2 and the lower electrode 3 as shown in FIG.
s, duration 20 μs, frequency 6 kHz, electric field strength 80
A kV / cm pulse electric field was applied to generate normal pressure plasma, and the proton conductive membrane was treated for 5 seconds.

As a result of analyzing the surface state of the proton conductive membrane before and after the treatment using an X-ray photoelectron spectrometer (XPS),
Before the treatment, the amount of sulfur on the surface was below the detection limit.
atom%. The static contact angle of the surface of the proton-conductive membrane after treatment with water was measured, and it was found that the surface was hydrophilized.

Comparative Example 1 A treatment was performed in the same manner as in Example 1 except that argon in the mixed gas was changed to helium, and the electric field intensity was changed to 10 kV / cm. The surface state of the proton conductive membrane after the treatment is represented by X
As a result of analysis using a line photoelectron spectrometer (XPS), the amount of sulfur on the surface was 0.1 atom%, the static contact angle of water on the surface of the proton conductive membrane after treatment was high, and sulfonation proceeded. No hydrophilicity was imparted.
In addition, in the case of using helium, when an electric field more than this was applied, the state was shifted to arc discharge.

Comparative Example 2 Instead of the pulse electric field, a sin having a frequency of 12.2 kHz was used.
Processing was performed in the same manner as in Example 1 except that a voltage having a waveform was applied, but the electric field intensity required for generating discharge was 100 kV.
/ Cm, and the discharge state was arc discharge, so that holes were formed in the proton conductive membrane.

[0049]

According to the present invention, the sulfonation treatment can be performed at high speed and at low cost without damaging the proton conductive membrane for a fuel cell, and sufficient hydrophilicity can be imparted. Therefore, it greatly contributes to the practical use of the fuel cell.

[Brief description of the drawings]

FIG. 1 is a waveform diagram showing an example of a pulse voltage applied between counter electrodes.

FIG. 2 is an explanatory diagram of a pulse duration.

FIG. 3 is a diagram schematically illustrating a configuration of an atmospheric pressure discharge plasma processing apparatus used in an example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Processing container 2 Upper electrode 3 Lower electrode 4 Pulse power supply 5 Gas supply device 6 Oil rotary pump 7 Unwinder 8 Winder 9, 10 Feed roll 11 Substrate inlet 12 Substrate outlet 13 Gas inlet 14 Gas exhaust Outlet P proton conductive membrane

Claims (3)

[Claims] 1. A proton conductive membrane for a fuel cell, comprising a proton conductive membrane for a fuel cell which has been sulfonated by atmospheric pressure discharge plasma treatment. 2. The normal-pressure discharge plasma treatment includes a pair of electrodes facing each other, and a counter electrode having one or both of the opposite surfaces coated with a solid dielectric is provided with a sulfur oxide gas and oxygen. And / or a rare gas mixed gas atmosphere in the vicinity of the atmospheric pressure, with the proton conductive membrane for a fuel cell disposed between the opposed electrodes, and a pulse rising time of 20 μs or less between the opposed electrodes. Atmospheric pressure discharge plasma treatment is performed on the proton conductive membrane for a fuel cell by applying a pulse voltage having a duration of 1 to 50 μs, a frequency of 1 to 20 kHz, and an electric field intensity of 50 to 100 kV / cm. A method for sulfonating a proton conductive membrane for a fuel cell according to claim 1. 3. A fuel cell using a proton conductive membrane for a fuel cell obtained by the method for sulfonating a proton conductive membrane for a fuel cell according to claim 1 or 2.